Intertidal Zone

By Colleen and Shannon

Intertidal Zone

What is the Intertidal Zone?

Organisms of the Intertidal Zone

Video

Works Cited

What is the Intertidal Zone?

The Intertidal Zone

The intertidal zone, also known as the littoral zone, in marine aquatic environments is the area of the foreshore and seabed that is exposed to the air at low tide and submerged at high tide, in example the area between tide marks (Biomes of the World). This ocean biome is the closet one to dry land and air. The tides here are created by the gravitational pull between the sun, the moon, and the earth. This biome has many small pools that house the organisms here along with many rocks that vegetation grows on.This is an extreme environment to live in because there is also the lack of water at certain times of the day and many other reasons. The tides are constantly going in and out creating waves, which could cause organisms to get swept away if they are not anchored down. There are extreme temperatures depending how close the area is to the sun or if they are in especially cold areas. And lastly, there is a high salinity in the water because salt water gets trapped in pools and later evaporates, creating salt deposits. This environment is divided into different areas: the spray zone, the high tide zone, the middle tide zone, and the low tide zone.

The Spray Zone

The spray zone is the highest part of the intertidal zone. Also called the upper littoral, it gets very little water, just ocean spray. The only times there is a lot of water in the spray zone is when it is flooded with storms or there has been an unusually high tide. As a result there is little vegetation in this area. There are mostly lichens and algae that grow on the exposed rocks. Some other organisms that live here are barnacles, isopods, limpets, periwinkles, and whelks. These creatures all mostly live on the rocks.

The High Tide Zone

The top part of the rock is the high tide zone, the middle part is the middle tide zone, and the lowest part is the low tide zone.

The high tide zone, also called the upper mid-littoral zone, is only flooded during high tide. It has a high salinity and little water, so there is not much vegetation, like in the spray zone. But there are more organisms living here than the spray zone. The main organisms in this area are anemones, barnacles, brittle stars, chitons, crabs, green algae, isopods, limpets, mussels, sea stars, snails, whelks and some marine vegetation. And unlike the spray zone, there are rock pools in the high tide zone that house small fish and some seaweeds. Another very common creature here is the hermit crab. This crab can carry its home, it shell, which shelters it and stores water in it, making it more common than other types of crab.

The Middle Tide Zone

The middle tide zone has equal times for being flooded and dry during a tide cycle. It is also called the lower mid-littoral zone. Salinity levels are lower here because there aren't as many dry salt deposits. There are about two tides per day here, and higher wave action than the high tide zone and spray zone. There is much more vegetation here, mostly seaweed. Rock pools are more common here than in the high tide zone. As a result, there are more fish, shrimps, krill, sea urchins, and zoo-plankton.. Most organisms here are larger and there is a larger amount of diversity. Most creatures living here are anemones, barnacles, chitons, crabs, green algae, isopods, limpets, mussels, sea lettuce, sea palms, sea stars, snails, sponges, and whelks. You can see there are many more different types of organisms living here.

The Low Tide Zone

A nudibranch, also called a sea slug

The lowest zone of the the intertidal zone, this area is also called the lower littoral zone. This area is normally covered by water and is only dry during extremely low tide so most things living here would not survive well if they were dry too long.There is the largest diversity of life here and has the largest organisms. Salinity here is about the same as the open ocean, and because this a shallow wet area there is much vegetation here. Seaweeds dominate the vegetation and can grow quite large. There are many Other organisms here because there are few predators here due to the waves and shallow water. Some of the organisms in this area are abalone, anemones, brown seaweed, chitons, crabs, green algae, hydroids, isopods, limpets, mussels, nudibranchs, sculpin, sea cucumber, sea lettuce, sea palms, sea stars, sea urchins, shrimp, snails, sponges, surf grass, tube worms, and whelks.

Organisms of the Intertidal Zone

Abalone
Anemones
Barnacles
Brown seaweed

A brittle star

Brittle stars - These organisms are closely related to starfish. They move across the ocean floor with their flexible arms, of which they normally have five. These arms can grow up to 24 inches in length. The brittle star can regrow its arms unless it loses all of them.
Chitons
Crabs
Green algae
Hydroids
Isopoda
Limpets
Mussels
Nudibranchs - These organisms are also called sea slugs, and are well known for being seen with vibrant colors. They can live at any level in the ocean, but grow to their biggest sizes in warm shallow waters. These creatures are hermaphrodites, like many slugs and most are carnivorous. They eat sponges, some other sea slugs, and even nudibranchs. Nudibranchs are found in almost every color which is used for camouflage.
Periwinkles - These are small edible species marine gastropod with gills and an operculum in the family Littorinidae. They are mostly found on rocky shores in the middle and higher tide zones. They are also found in small pools and sometimes in muddy parts of estuaries. This organism is mostly an algae grazer, but will also eat things such as barnacle larvae.